Method of producing iron or steel alloys



Patented May' 10, 1932 UNITED STATES PATENT. OFFICE nnnmne GUSTAV nonmAND EMIL GUSTAF monvnnzo sosrnrsson, or s'rocxnonnr,

. swnnnn METHOD or PRODUCING men on. STEEL ALLOYS The present invention,which is a contion Serial No. 7 56,823, filed June 24, 1926, relates toa method for producing alloys of metals belonging to the iron group, andespecially alloys of iron, directly out of oxide ores of said metal andoxide ores of the al loy constituents, with the use of carbon as areducing agent. The carbon, if desired, may

be partly replaced by other reducing agents such as ferro-silicon,ferro-manganese o aluminium.

The expression alloys of iron comprises all alloys containing iron,ranging from, on the one hand, alloys in which iron is the mainconstituent, that is to say, iron or steel which in addition to the ironcontains one or more other metals which impart special desirableproperties to the iron, such properties being such as are not possessedby carbon-iron or carbon-steel alone; to, on the other hand, alloys inwhich iron ispresent to a relatively less extent as in, for example,ferro-manganese, ferro-chromium, ferro-manganesesilicon, or the like. Ia e In iron works it often happens that in one heat or smelting analloyed iron or steel containing a certain percentage of, for instance,chromium, is to be produced and that in a following heat an alloyed ironor steel containing a different percentage of chromium will have to bemanufactured. In such cases it has been necessary, prior to ourinvention disclosed in said copending application and prior to thepresent invention, to make up a special charge for every differentpercentage of chromium in the alloyed metal, which, of course, requiresseveral corresponding charges of difierent compositions. It has alsobeen proved to be rather difiicult to regulate the percentage of alloyconstituent within narrow limits by simply varying the composition ofthe charge.

The method disclosed in our copending application, Serial No. 7 56,823,of which this No Drawing. n Application filed July 26, 1929, Serial No.381,382, and in Sweden September 24, 1924.

is a continuation, obviated the above inconvenience to such extent thatit represented a distinct advance in the art. The method consistedchiefly in making up separate mixtures of finely ground portions of eachone of the oreswith carbonaceous material of a quantity proportioned tothe reduction of the ore and to the desired percentage of carbon in thefinal product, and'melting these mixtures in a furnace, with thequantities of the mixtures so proportioned to' each other as to obtainan alloy of the desired composition.

Now it is well known that chromium ore,

when reduced by carbonaceous reducing agents, always produces a productwhich is more or less contaminated with carbon, so that furtherrefinement iswnecessary. For this reason, inventors and experts in themetallurgical art have, prior to our inventions, found it necessaryfirst to produce a highcarbon product, and thereafter to remove theexcess carbon by the addition of ore or by other means. These two-stageprocesses are necessarily costly and result in. a considerable loss ofalloying metal.

It is the principal object of the present invention to perfect theprocess disclosed in our application, Serial No. 756,823 and brieflydescribed above so that the foregoing disadvantages will be entirelyobviated. This we have done and we are able at will to producepredetermined low carbon alloys directly while using a carbonaceousreducing agent. 'Our improved process will now be described in detail.

The invention comprises forming separate mixtures of the oxide ore ofthe base metal, forinstance, iron, and of the oxide ore of the alloyconstituent together with carboncontaining reducing agent of a quantitypro portioned to the reduction of the ore and to the desired percent-ageof carbon in the metal therefrom and reducing and melting said mixtures'whilst floating on top of or in a slag bath in an electric furnacewhilst pro- 35* I -1 ing a more solid adhesion of the grains, ad-

'- quantity ofcarbon useful for the reduction portioning the quantitiesof the'mixtures to each other so as to obtain an alloy of the desiredpercentage of the alloy constituent.

The expression carbon-containing reduc ing agen is understood tocomprise, on the one hand, all sorts of carbon, for instance, char-coal,pit-coal, anthracite, coke or the like; on the other hand, however, alsoany mixture of carbon with another reducing- I agent'or agents, such asferro-slhcon, ferromanganese, ferro-aluminium-silicon, aluminium or thelike, provided such other reducing agent be added only in suchproportion, that the carbon is the main constituent and that the processwill remain endothermic.

While the mixtures may consist of finely ground and intimately mixedloose material,

we prefer to transform each of "them into a solidified state by mixingtge-corresponding oxide ore in a finely divi ed state withcarbon-containing reducing agent in a finely divided state andtransforming said mixture into. briquettes or any other'form of bodiesin known manner. The smaller the size. of the grains of the ore andparticles of the reducing agent, such as carbon, that is to say, thecloser the size of the grains approaches the molecular size the betterthe method is effected. .In the briquettes the particles of the reducingagent and the grains l of the ore should be distributed as unifor mly aspossible and the mass should be of such consistency as will preventsegregation of its constituents.

v If required or found suitable for obtainhesive's of known kind may beused in the process of transforming the materials into solidified statebut in such case, provided carbonaceous adhesives are used, thetotal 1nthe various kinds of charge should be so adapted. that the desiredpercentage of carbon is obtained in the final product. p In someinstances the charges or briquettes are dried prior to being introducedinto the electric furnace, in'air or some other atmosphere,

.for instance, an atmosphere-containing'carhome acid, when usmghme orlime-white as an adhesive and areagent. Thus, if liq- 'uid'carbonaceousreducing material or liquid adhesive has been added, the mass will bedried so that these'materials become solid and keep the particles of theore and those of the reducing agent together in fixed relation. By thedrying process any contents of water that may be present are expelled,

so that bursting of the briquettes or bodies through steam developed bythe heat in the furnace cannot take place.-

If, to facilitate a very intimate mixing of the particlesof the ore withthose of the reducing agent and any adhesive added,-a

certain percentage of water has to be added, it may be preferred only topartially dry the mixture prior to the briquetting process which is bestcarried out with a certain percentage of water in the mixture.

Obviously, if a plurality of metals are to be alloyed with the iron,separate charges,

preferably in the form of solidified bodies, may be prepared from theores of each of said metals, or a charge may be prepared from a suitablemixture of these ores.

Y The charge of the base metal, for instance, iron ore, may bereduced'and melted in ad-v sition of the final productand it will thenbe found easy during working to take tests to ascertain whether thedesired proportions have been obtained, andiby an increased addition ofthe one or the other kind of charge to control the final composition ofthe product. Y

' Of course, such afurnace practice may also be applied when reducingand melting an admixture of different kinds of charge. Thus, bycontrolling the quantity fed in of each kind of charge, alloys havingdifferent percentages of the alloyin metal or metals may be readilyproduced wit out varying the composition of each kind of charge. If onlya small quantity of other metal is to be alloyed with the base metal, itis preferred first to reduce the base 'metal out of the base metalcharge in the manner set forth, and then to reduce the metal or metalsto be allo ed with the base metal out of the alloy 0 arge or charges.Withgreater percentages of alloying metal that order is used between thedifferent kinds of charge which is found most advanta eous in eachindividual case.

In or inary cases .deoxidizing of iron or 1 steel is effected by theaddition of deoxidizing metals, generally ferro-manganese orferrosilicon or both, in a metallic state, and such deoxidation may beapplied also to our present process at any desired time during asmelting. It is preferred, however, to prepare bri uettes or otherbodies in the-manner previous y set forth, out. of oxide ore of ametaladapted to be used as a deoxidizing agent, especiallymanganese,such briquettes a being reduced and melted on the slag bath in thefurnace when deoxidation of metal orslag or both is to be effected. Thedeoxidizing metal reduced in this process then removes from the alloypreviously obtained in the furnace aigreater or smaller part of itsoxygen, and is transferred into the slag bottom of the furnace. Inproducing, for in stance,so called rustless iron andv steel holding9-16% Cr and below 0.7% 0., the consumption of chromium charge for agiven quantity of alloy will be considerably smaller if reduction iseffected in the manner set forth. 7 Ifnot, such reduction will takeplace with the chromium first reduced out of the chromium charge, whichchromium is thus lost in the slag. As the chromium ore is much moreexpensive per unit of oxygen absorbed tric resistance heat developed inthe slag,

from the slag than is; for instance, manganese ore, a considerable.saving will be attained in this manner.

'The reduction and melting should preferably take place with theelectrode or electrodes out of contact with the charge or charges,especially'when using carbon electrodes, and by the aid, at least inpart, of eleift. e charge or charges being reduced and melted whilstfloating on or in said slag as is more fully described in our Patent No.1,686,206. The present invention takes the process of that applicationseveral steps further, in that, instead of one charge, two or morecharges are used, for example, an iron charge and a chromium charge, andthese two charges are so proportioned to each other as to produce thedesired alloy directly. Our success in producing these alloys,particularly the lower carbon alloys, such as stainless iron, directly,where prior inventors have failed, appears to be due in great part tothe fact that in the present process the charge is reduced and meltedwhile floating on the top of or in a slag bath .in an electric furnace.with the aid, at least in part, of electric resistance'heat developedin the slag and that the particles of ore and carbon are mixed incorrect proportions in intimate contact with one another, which contactis maintained during the course of the reaction.

In reducing and melting the different kinds of chargein succession, itis preferred in some cases, after one kind of charge has been reducedand melted wholly or partly to draw off the slag thus formed out of'thefurnace,

before treatment of the next kind of charge is commenced. The reasonsfor this are different. In ores of comparatively expensive metals, aconsiderable saving may be attained in this manner, owing to slagging ofthe expensive metal to a less extent, in that a smaller quantity of slagthan otherwise'is saturated in the furnace with oxides of this metal. If

some or more of the oxide ores holdsulphur' to such an extent thatthe-percentage of sulphur in the metal produced would be higher thandesirable, it is preferred first to reduce and to melt the charge orcharges containing this ore or these ores respectively, and then whollyor partly to draw ofi the slag obtained for removing the sulphurabsorbed in the same. Prior to tapping the slag the same may bedeoxidized in the manner hereinabove set forth, or in some other way,for instance, by the addition of lime and carbon and by working with theelectric arc, so that carbide of calcium is formed, in order to reducethe percentage of-metal of the slag, and to increase its capability ofabsorbing sulphur. By tapping the slag intervening with the melting ofthe diiferent kinds of charge, the phosphorus transferred into the slagmay also be removed from the furnace, before the same would, perhaps, bereduced. and absorbed. in the metal in the treatment of the other kindof charge. By controlling the total percentage of carbon in thedifferent kinds of charge, a product having thedesired percentage ofcarbon may be produced directly. The desired percentage of carbon in theproduct may also, however, be obtained by controlling the percentage ofcarbon in the kind of charge out of which a metal havinga low percentageof carbon may be most readily produced, thus, for example, in the ironore charge,- so that a metal having a low percentage 0 carbonis firstobtained, that is to sa iron, in the example given, and by then ad ingthe other kind or kinds of charge having a percentage of carbon soadapted that the final product will have the desired percentage ofcarbon. If, however, products having difierent percentages of carbonareto be produced, it is more simple to use chargesdn which the totalquantity of carbon has been adapted so that a product of alloyed iron orsteel or an alloy as low in carbon as possible is obtained which is thencarburized to the desired percentage of carbon in the furnace or outsidethe same. Preferably this carburization may also be effected.

by introducing into the furnace and by reducing and melting, in'a finalprocess, a certain furnace, either in the furnace or outside the same,for instance in a ladle or another furnace. In the same manner, an ironalloy or the like having approximately the proper percentage of thedesired alloy substances,

such iron alloy beingproduced directly out of oxide ores according tothe invention,

may preferably beadmixedwith such alloy substances in a metallic statein known manduced at a much lower cost than in the meth ods heretoforepractised for the production of such alloyed'irons and steels. In ordernot to attain too high percentages of carbon in the final product, thealloy substances, as a matter of fact, hitherto had to be added to theiron in the form of very expensive low- 'rustless.

carbon alloys of these substances, With the application of this method,for example, so called rustless iron or steel, that is to 'say an ironhaving a rather high percentage 0 chromium or about 916%, and a ratherlow percentage of carbon, or below 0.7%, may be produced directly. Nodifliculty will be experienced with this method in directly roducing aniron holding, for instance, a out 14% Cr and below 0.1% C.which,withoutfurther treatment may directly be regarded as In the production of suchrustless iron it has been found particularly suitable to use lime-whiteas anadhesive, either in the iron ore charge or in the chromium orecharge, or in both kinds of charge. The reason for this is that thechromium ores contain, as ..a rule, a large quantity of magnesia, whichmakes the slag produced viscous unless'a com- %aratively largequantityzoflime is added. y the addition of lime-white, an almostcomplete desulphurization of the metals 'is obtained at the same timewhile reducing and melting the charges of the two kinds of ore,

inasmuch as the lime' covering'thegrains as a film absorbs the sulphurwhile forming sillphideof calciumwhich is absorbed in the s ag.

' In order to form a suitable slag in the fur?- nace for the reductionand the melting of the diflerent kinds of charge, requisite fluxes maybe admixed either in a finely divided state in preparing thedifierentkinds ofcharge, or, such fluxes may be directly'introduced into process.4

The followingis a specific example of the proportioning of the chargesin accordance with our invention for the production of socalled rustlessiron, it being understood, how'- ever, that the invention is not limitedto the composition of the to herein. For the production of rustlessiron, an iron charge and a chromium charge are used hav difi'erentcharges referred the following composition in part by The charges areboth prepared of finely divided ore, preferably of such a grading as tobe able to pass a sieve having at least 550 meshes per cmF, and finelydivided charcoal of the same rading; The lime is preferably used in theorm of lime-white and act s as a binding agent. After the materials havebeen accurately mixed and the mixture brought into briquettes or otherpieces, the charges are carefully dried. The iron charge is 'then fedinto the electric furnace and reduced and melted whilst floating on orin a slag bath in saineby the aid, at least in part, of electricresistance heat developed in said slag bath, an iron 'very low in carbonbeing then obtained on the bottom of the furnace, whereas the slagbecomes rather rich in ferrous oxide. The greater part oftheslag is thenta ped ofi and the sla may be deoxidize for instance by intro ucing intothe furnace. briquettes or other bodies of man-v ganese ore andcarbonaceous material, for the purpose of saving chromium. The chromiumcharge is then fed into the furnace and reduced and melted in the samemanner as the iron charge. In order to utilize chromium oxlde containedin the slag, a suitable quantity of a thermal reducing agent, preferablyferro-silicon, may be added to the slag. By suitably adapting thequantity of the chromi- 11m charge'in relation to that of iron char e,an iron having the content of chromium e slred will directly obtained. 3

If, on the other hand, stainless steel is to' be produced, the carboncontent in one of the tended contentsof chromium and carbon.

the furnace. Preferably, the admixture 'of flux is then adapted so thata slag is obtained which is suited to each separatereduction:

. from oxide ore of said metaland oxide ore- What we claim is:--- i g 1.A method of producing an alloy of a metal belonging to the iron groupdirectly of the alloy constituent or constituents, which, in a groupofstep'sfincludesforming separate mixtures ofach 'ofsaidores with anamount of carbon-containing reducingagent propor-,

tioned to the'reductionof the ore and'to the v desired percentage ofcarbon in'the, alloyobt aihed erefrom, briquetting said mixturesseparately, '-and reducing and melting said i briquettes on a slag bothan-clectric furnace whilst proportioning the quantity of briquettes ofeach kind so as to obtain an alloy of the desired composition.

7 2. A method of producing an alloy of a metal belonging to the irongroup directly from oxide ore of said metal and oxide ore of the alloyconstituent or constituents,

which, in a group of steps, includes forming separate mixtures of eachof said ores with anamount of carboncontaining reducing agentproportioned to the reduction of the ore and to the desired percentageof carbon in the alloy obtained therefrom, briquetting said mixturesseparately and reducing and melting on a slag bath in an electricfurnace briquettes of each kind one after the other in order to providefor adapting the working conditions of the furnace to each kind of different'ores whilst proportioning the quantity of briquettes of each kindso as to obtain an.

alloy of the desired composition.

3. A. method of producing an alloy of a metal belonging. to the irongroup directly from oxide ore of said metal and oxide ore of the alloyconstituent or constituents, which, in a, group of steps, includesforming separate mixtures of each of said ores with an amount ofcarbon-containing reducing agent proportioned to the reduction of theore and to the desired percentage of carbon in the alloy obtainedtherefrom, briquetting said mixtures separately, reducing and meltingsaid briquettes on a slag bath in an electric furnace whilstproportioning the quantity of briquettes'of each kind in order toproduce an alloy of the desired composition and deoxidizing the alloyproduced and the slag by reducing and melting in the presence thereofbriquettes containing an intimate mixture of finely divided oxide ore ofa deoxidizing metal and finely divided carbonaceous material, thislatter being added in a quantity proportioned to the reduction of saidore.

4. A method of producing an alloy of a metal belonging to the iron groupdirectly from oxide ore of said metal and oxide ore of the alloyconstituent, which, in a group of steps,includes forming separatemixtures of each of said two ores with an amount of carbon-containingreducing agent proportioned to the reduction of the ore and to thedesired percentage of carbon in the alloy obtained therefrom,briquetting said mixtures separately, reducing and melting first onlyone kind of briquettes on a slag bath in an electric furnace, tappingthe slag formed during said redu'ction process and adding, reducing andmelting the other kind of briquettes Whilst proportioning the quantityof briquettes of steps, includes forming separate mixtures of each ofsaid two ores wlth an amount of carbon-containing reducing agentproportioned briquettes of either one or the other kind andtherebyprovide the exact percentage of metal contents in the final product.

6. A methodof producing rustless iron or stainless steel directly fromiron oxide ore and chromium oxide ore, which, in a group of steps,includes forming separate mixtures of each bf said two ores with anamount of earbon-containing reducing agent proportioned to the reductionrequirements of the ore and to the desired percentage of carbon in thealloy obtained therefrom, briquetting said mixtures separately andreducing and melting said briquettes on a slag bath in an electricfurnace whilst proportioning the quantity of briquettes of each kind inorder to provide an iron alloy containing the desired percentage ofchromium.

7. A method of producing an alloy of a metal belonging to the iron groupdirectly from oxide ore of said metal and oxide ore of the alloyconstituent or constituents, which, in a group of steps, includesforming separate mixtures of each of said ores with a carhon-containingreducing agent, the percentage of carbon in the mixture containing theore of the main alloy constituent being proportioned so that thepercentage of carbon in the metal reduced from this mixture will belower than the percentage of carbon in the final product, briquettingsaid mixtures separately, reducing and melting said briquettes on a slagbath in an electric furnace whilst proportioning the quantity ofbriquettes of each kind in order to provide an alloy of the desiredcomposition and carburizing the mixture, whereby to obtain the desiredpercentage of carbon in the final product.

In testimony whereof, we have hereunto set our signatures.

HENNING GUSTAV FLODIN. EMIL GUSTAF TORVALD GUSTAFSSON.

each kind in order to produce an alloy of the 1 desired composition.

5. A method of producing an alloy of a metal belonging to the iron groupdirectly from oxide ore of said metal and oxide ore of the alloyconstituent, which, in a group of

